1. Field of the Invention
The present invention relates to a zoom lens system, and in particular, relates to a wide-angle zoom lens system that is favorable for use in a single-lens reflex camera. In addition, the present invention relates to an intra-lens image-stabilizing zoom optical system in which part of the lens system thereof can be decentered in order to correct image-blur caused by vibrations/hand-shake, etc.
2. Description of Related Art
Since it is relatively easy for a so-called “negative-lead zoom lens system”, in which a lens group having a negative refractive power is provided closest to the object side, to obtain a wide angle-of-view and a long backfocus relative to the focal length, negative-lead zoom lens systems are often utilized in wide-angle zoom lens systems for use in a single-lens reflex camera.
A number of negative-lead zoom lens systems have been proposed in which an image-stabilizing function (image-shake correcting function) is installed, which corrects deviations in the imaging position caused by vibrations/hand-shake, etc., by decentering part of the lens system thereof in a direction orthogonal to the optical axis direction (refer to Patent Literature 1 through 4 indicated below).
In such intra-lens image-stabilizing zoom optical systems, aberrations such as decentration coma, in a state where a image-stabilizing lens group is decentered, and image plane tilt, etc., are required to be favorably corrected, and aberration fluctuations occurring during an image-stabilizing drive operation are also required to be reduced.
In regard to such requirements, in order to apply the image-stabilizing zoom lens systems disclosed in Patent Literature 1 through 4 to a highly-pixelized digital camera, etc., which requires a relatively high optical quality, the correction of aberrations during an image-stabilizing drive operation (during decentering of an image-stabilizing lens group) and the optical quality are insufficient.
In order to improve the optical quality of the zoom lens system during an image-stabilizing drive operation, it is effective to increase the freedom in design of the image-stabilizing lens group and to reduce the occurrence of aberrations within the image-stabilizing lens group by increasing the number of lens elements thereof or by utilizing at least one aspherical surface therein.
However, if the number of lens elements of the image-stabilizing lens group are increased too much, the burden on the drive mechanism for the image-stabilizing lens group increases, and also causes enlargement of the entire zoom lens system (and also the entire apparatus which includes the drive mechanism of the image-stabilizing lens group). Furthermore, an increase in the number of lens elements in the image-stabilizing lens group and the use of lens elements having at least one aspherical surface become a cause for increasing the manufacturing costs.
On the other hand, such negative-lead wide-angle zoom lens systems for a single-lens reflex camera are known to be configured of a negative first lens group, a positive second lens group, a negative third lens group and a positive fourth lens group, in that order from the object side (refer to Patent Literature 5 through 10 indicated below).
Generally, in a wide-angle zoom lens system, since abaxial aberrations such as distortion, field curvature, astigmatism, and lateral chromatic aberration, etc., occur together with a zooming operation or a focusing operation being carried out, it is difficult to obtain a high optical quality over the entire focal length range and over the entire photographing distance range.
In regard to this matter, the zoom lens systems in Patent Literature 5 through 10 are no exception; in order to apply the zoom lens systems of Patent Literature 5 through 10 to a highly-pixelized digital camera, etc., which requires a relatively high optical quality, the optical quality thereof is insufficient, and aberration fluctuations, which accompany a change in focal length or photographing distance, are required to be favorably corrected.